[sdiy] (no subject)

[Mike Pepper]

> I have recently decided to use some SMT tempcos with wire tails in lieu
> of 'proper' through-hole resistors on VCOs.
>
> Some of the SDIY gang have used epoxy resin to encapsulate SMTs in this
> sort of application to provide some physical strength, is there any
> evidence of the set epoxy changing the component properties? Has anybody
> actually checked?
>
> I ask this because decades ago, I read about a tiny radio transmitter
> working fine until epoxy encapsulated and the fault being blamed on the
> resin 'crushing' the components as it cured and altering the tuning, I
> cannot remember if the faultfinding revealed if it was caps, coils, or
> whatever and I am only interested in the tempco here so it could be
> irrelevant.
>
I've had some success with mounting an SMD tempco on a 'crumb' of PCB and
fitting this underneath the matched pair, (using SSM2210), in the void of
the 8 pin DIL socket. I put a bit of hard foam under the little scrap of pcb
material, to ensire a good thermal conract when the chip was inserted.

I like the idea because I also think that smaller tempcos, having less
thermal mass may be more prone to draughts or random air movement,which
wouldn't afffect the semiconductor that they are compensating. This way they
are screened below the chip, and the chip can be removed as usual. If you're
going to solder the chip in, just put the tempco under it.

I was able to do the same with the smaller wire ended tempcos in my Jurgen
Haible 'Living VCOs', because the 14 pin Turned pin sockets I used for the
CA3046's had suitable grooves in the end moulding.

A thought, anyway.

Mike